Poly(thieno[3,4-b]thiophene) (PTT) based transparent conductive polymers have been developed for hole injection layer (HIL) applications in polymer light-emitting devices. Using a second generation material that uses a poly(perfluoroethylene-perfluoroethersulfonic acid) as polymeric dispersant/counter-ion (PTT:PFFSA), significant improvement (up to 6 times with LUMATION Green 1304 as the light emitting layer) in PLED lifetime has been achieved compared to the lifetime of first generation PTT:PSSA (PTT:poly(styrene sulfonic acid)) based devices. Compared with the work function of 5.2 eV for PTT:PSSA film, PTT:PFFSA films have a higher work function of 5.5~5.7 eV. Interestingly, we found that the resistivity of PTT:PFFSA films is dependent on the film preparation conditions such as annealing temperature and time; while the work function of PTT:PFFSA films is independent on the film annealing conditions. We also studied the dependence of the device leakage current and lifetime on the preparation conditions of PTT:PFFSA based HIL films. Higher HIL annealing temperature results in higher device leakage current mainly due to the lower resistivity of the PTT:PFFSA HIL film prepared under such condition. However, the device lifetime is almost independent on the annealing temperature in the studied temperature range from 130 to 210°C using dispersions with PFFSA-to-TT ratios of 12:1 and 18:1.
The interface between the hole transport layer (HTL) and emissive layer (EML) in polymer light-emitting diodes (PLEDs) has attracted intense research attentioin since the initial discovery of PLEDs in 1989. In this contribution, we analyze the electron-blocking properties of various HTL at this interface and their effect on PLED device performance. We find that poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) - a conventional PLED HTL - does not possess optimum electron-blocking properties and that PLED device performance can be significantly enhanced by inserting a new type of electron-blocking layer (EBL) between the PEDOT-PSS HTL and EML. The new EBLs developed in this study consist of two major components: a siloxane-derivatized, crosslinkable, TPD-like triarylamine hole-transporting material, such as 4,4’-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi2), and a hole-transporting polymer, such as poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl) diphenylamine) (TFB). TPDSi2 undergoes crosslinking in air and rendering the TPDSi2 + TFB blend insoluble. With the TPDSi2 + TFB EBL inserted between PEDOT-PSS and BT layers, PLED device current density is reduced, device light output and current efficiency are dramatically increased (maximum current efficiency ~ 17 cd/A). Our result shows: 1) insufficient electron-blocking by PEDOT-PSS is another reason for the poor performance of PEDOT-PSS/BT based devices; 2) PLED device performance can be dramatically enhanced with a triarylamine siloxane-based EBLs.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.